In many integrated circuits (ICs), multiple components are powered from a voltage supply, which may be at a supply voltage level, e.g., VDD. Because there can be multiple devices in the IC, if the voltage at a node coupled between two devices is below a certain level, the first device may be damaged. Where the node voltage is above another level, the second device can be damaged. Note that the damage may not cause a catastrophic failure but instead may be a reliability issue so that lifetime of the product is compromised.
In addition, for many components of an IC, this VDD level is large enough to damage the components. To enable specific devices/circuits on the chip to be powered from a lower level voltage, various voltage regulators or converters may be present. Such regulator circuits can be specifically designed to protect other circuitry with given functionality and having a maximum voltage level less than the supply voltage, VMAX<VDD.
Common implementations of such a circuit may include a switching (lossless) power converter, either synchronous or asynchronous, a linear regulator or a low-dropout linear regulator (LDO). In certain ICs an LDO can be used to protect a variety of circuits. As circuits that are coupled to receive a regulated voltage, Vreg, perform their tasks, they draw variable amounts of current from VDD. For any non-perfect controller in the regulator this means that Vreg is imperfectly regulated.
In other words, changes in the load circuitry can cause glitches on Vreg. For example, instantaneous jumps in the amount of quiescent current drawn from the supply can cause glitches. Many ICs include or are coupled to a significant capacitor on the Vreg node. In a typical LDO design, this capacitor supplies instantaneous current demands, thus smoothing out the glitches. For example, to smooth out glitches this capacitor may need to be on the order of microfarads (g), which may be far too large to implement on chip for many IC designs. Thus, this capacitance either consumes significant on-chip real estate, or if implemented off-chip, costs a pin of the IC and increases a bill of materials.